Za Dengel may have been married to Woizero Wangelawit, eldest daughter of his second cousin Susenyos (later emperor) and lady Wolde Saala of Walaqa and Marabete (later Empress Sultan Mogassa).

Sarsa Dengel had intended to make his nephew as his heir, recognizing that to avert the civil war that would likely follow his death an adult would be needed, and the emperor's own sons were quite young. These plans were changed primarily through the influence of Empress Sena Maryam, stepmother of Emperor's eldest surviving son Prince Yaqob, who was made emperor in 1597. The empress had Za Dengel seized and confined in a religious retreat on the island of Dek in Lake Tana. Za Dengel eventually managed to escape, taking refuge in Gojjam.

In 1603 Za Dengel was made Emperor by RasZa Sellase, who intended Za Dengel to be little more than a figurehead. He was crowned as Asnaf Segad ('He to whom the horizons bow'). However, Za Dengel summoned the JesuitPedro Páez to his court at Dankaz, who persuaded him to embrace Catholicism.

This religious conversion led to Za Sellase not only withdrawing his support, but actively working against him and stirred up a revolt in Gojjam. Za Dengel marched to the plain of Bartcho to put down this revolt, but despite the help of 200 Portuguesemusketeers Za Dengel perished in battle on October 24. According to James Bruce, Za Dengel's corpse lay unclaimed on the battlefield for three days, until some peasants buried it "in a little building, like a chapel (which I have seen), not above six feet high, under the shade of a very fine tree, in Abyssinia called sassa." The body was reinterred 10 years later in Daga Estifanos monastery on Daga Island in Lake Tana.[1]